1. Field of the Invention
The present invention relates to dynamic path selection for determining an optimum path on the basis of link metric and, more particularly, to a network load distribution system which realizes load distribution of the entire network through monitoring of a state of the network by a network management server to periodically update link metric to be optimum.
2. Description of the Related Art
At data transmission in a network, selecting one of a plurality of communication paths which can reach a transmission destination is referred to as path selection (or routing). Various methods are employed as path selection in order to select an optimum path aiming at reducing a transmission time and improving use efficiency of a transmission path.
Static path selection is a system of in advance fixing a communication path regarded as an optimum path for each transmission destination. Communication path for each transmission destination is designated at a routing table whose reference realizes path selection.
Dynamic path selection is a system of updating the contents of a routing table to be optimum according to a traffic change and a change of a network structure. By exchanging the routing tables among nodes by using a routing protocol, information of other nodes is obtained to conduct optimum path selection.
The number of relaying devices on a communication path is called xe2x80x9chop valuexe2x80x9d which represents a distance between transmission and reception nodes using the communication path. Then, the actual number of relaying devices on a path passing through the minimum number of relaying devices is called xe2x80x9ccostxe2x80x9d. These arrangement realizes optimum path selection using a link metric, that is, a distance on a network.
Main routing protocols are RIP (Routing Information Protocol) and OSPF (Open Shortest Path First).
RIP determines an optimum path based on a hop value and a cost. However, even if a cost, that is, the number of relaying devices is minimum, a transmission time is not always the shortest. OSPF resolves these shortcomings of RIP and determines an optimum path taking a congestion state of a line into consideration.
In conventional network load distribution systems using dynamic path selection of this kind, each node on its own measures a load of a link between the own node and its adjacent node and when the load exceeds a certain threshold value, a link metric is appropriately increased or decreased according to rules determined in advance, a routing table is responsively updated, and the change of the link metric is notified to other node within the network.
Japanese Patent Laid-Open (Kokai) No. Heisei 05-130144 recites a system including a link load state detection unit and a link metric change and transmission unit.
As described in the foregoing, conventional network load distribution systems have the following shortcomings.
First problem is that conventional network load distribution systems are directed to local load distribution only in the vicinity of each node and not optimum load distribution in the entire network. The reason is that since based on a load of a link between each node and its adjacent node (that is, load of only the nodes in the vicinity) that each node measured on its own, a link metric between each node and the adjacent node is appropriately increased or decreased locally, only local load distribution is realized and not load distribution taking conditions of the entire network, in addition to the adjacent nodes, into consideration.
Secondly, the related art laid open in the above-described Japanese Patent Laid-Open (Kokai) No. Heisei 05-130144 fails to determine an optimum link metric according to a dynamic change of the entire network. The reason is that since the network load distribution system recited in the above Japanese Patent Laid-Open No. 05-130144 employs a simple static method of increasing or decreasing a link metric of a link, for example, when a load of the link exceeds a specific threshold value, it is impossible to realize load distribution according to a topology change, a traffic distribution change or other change related to the entire network.
A first object of the present invention is to provide a network load distribution system enabling optimum load distribution taking the entire network into consideration in order to improve transmission efficiency, reliability and performance of the network.
Another object of the present invention is to provide a network load distribution system allowing determination of an optimum link metric and updating of a routing table in accordance with dynamic changes related to the entire network such as a network topology change and a traffic change.
According to one aspect of the invention, in a network having a plurality of nodes connected to each other with links,
a network load distribution system including a load distribution server for receiving network state information from the plurality of nodes and determining an optimum link metric based on the network state information to transmit the optimum link metric to the plurality of nodes, wherein
dynamic path selection is conducted at each node based on the optimum link metric.
In the preferred construction, the network state information includes network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node.
In another preferred construction, the network state information includes network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, link load information indicative of a use band and a maximum usable band on each the link adjacent to the node in a direction of transmission from the node, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node.
In another preferred construction, the load distribution server includes a path selection emulator for emulating operation of path selection for all of the nodes in the network, the path selection emulator, while referring to the network state information and changing a value of a link metric in the path selection emulator, repeatedly conducting emulation to obtain the optimum link metric.
In another preferred construction, the network state information includes network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node, and
the load distribution server includes a path selection emulator for emulating operation of path selection for all of the nodes in the network,
the path selection emulator, while referring to the network state information and changing a value of a link metric in the path selection emulator, repeatedly conducting emulation to obtain the optimum link metric.
In another preferred construction, the network state information includes network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, link load information indicative of a use band and a maximum usable band on each the link adjacent to the node in a direction of transmission from the node, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node, and
the load distribution server includes a path selection emulator for emulating operation of path selection for all of the nodes in the network,
the path selection emulator, while referring to the network state information and changing a value of a link metric in the path selection emulator, repeatedly conducting emulation to obtain the optimum link metric.
In another preferred construction, the load distribution server obtains the optimum link metric by repeatedly conducting the emulation by means of the path selection emulator while changing a value of a link metric in the path selection emulator such that the amount of a link load of each the link in the network is equal to each other.
In another preferred construction, the load distribution server obtains the optimum link metric by repeatedly conducting the emulation by means of the path selection emulator while changing a value of a link metric in the path selection emulator such that a value obtained by dividing the amount of use bands of each the link in the network by the amount of real link bands is equal to each other.
In another preferred construction, for the dynamic path selection, at each the node, a routing table of the node is updated based on the optimum link metric and furthermore, the optimum link metric is notified to and from other the node adjacent to the node by a routing protocol to update the routing table based on information from the adjacent node.
In another preferred construction, one or a plurality of the nodes in the network have the load distribution server provided therein.
In another preferred construction, one or a plurality of the nodes in the network have the load distribution server provided therein,
the load distribution server notifying the node having the load distribution server provided therein to each of other nodes not having the load distribution server provided therein by the routing protocol to recognize a position of the load distribution server.
In another preferred construction, one or a plurality of the nodes in the network have the load distribution server provided therein, and
when the network is connection-oriented,
an existing connection is changed as well according to the optimum link metric at the time of notification of the optimum link metric to and from the adjacent node.
In another preferred construction, one or a plurality of the nodes in the network have the load distribution server provided therein,
when the network is connection-oriented,
an existing connection is changed as well according to the optimum link metric at the time of notification of the optimum link metric to and from the adjacent node, and
at the time of changing the existing connection, after newly establishing an optimum connection while leaving the existing connection as it is and making a detour for the service of the existing connection to the new optimum connection so as to prevent interruption of services by the existing connection, the existing connection is cut off.
According to another aspect of the invention, a load distribution method in a network having a plurality of nodes connected to each other with links, wherein
a load distribution server receives network state information from the plurality of nodes and determines an optimum link metric based on the network state information to transmit the optimum link metric to the plurality of nodes, and
dynamic path selection is conducted at each node based on the optimum link metric.
In the preferred construction, the network state information including network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node.
In another preferred construction, the network state information including network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, link load information indicative of a use band and a maximum usable band on each the link adjacent to the node in a direction of transmission from the node, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node.
In another preferred construction, at the load distribution server, a path selection emulator for emulating operation of path selection for all of the nodes in the network repeatedly conducts emulation while referring to the network state information and changing a value of a link metric in the path selection emulator to obtain the optimum link metric.
In another preferred construction, the network state information including network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node, and
at the load distribution server, a path selection emulator for emulating operation of path selection for all of the nodes in the network repeatedly conducts emulation while referring to the network state information and changing a value of a link metric in the path selection emulator to obtain the optimum link metric.
In another preferred construction, the network state information including network topology information indicative of a mode of connection of the node to each the adjacent node, link metric information indicative of a value of a link metric assigned to a direction of transmission from the node to each the adjacent link, link load information indicative of a use band and a maximum usable band on each the link adjacent to the node in a direction of transmission from the node, and traffic flow information indicative of a traffic characteristic and a traffic parameter at the node, and
at the load distribution server, a path selection emulator for emulating operation of path selection for all of the nodes in the network repeatedly conducts emulation while referring to the network state information and changing a value of a link metric in the path selection emulator to obtain the optimum link metric.
In another preferred construction, for the dynamic path selection, at each the node, a routing table of the node is updated based on the optimum link metric and furthermore the optimum link metric is notified to and from other the node adjacent to the node by a routing protocol to update the routing table based on information from the adjacent node.
Other objects, features and advantages of the present invention will become clear from the detailed description given herebelow.